With the development of technology, at present, cell phones, especially smart phones, have become indispensable electronic devices in people's daily lives. In addition, as people's daily requirements for cell phones become higher and higher, they desire cell phones capable of implementing more functions, such as supporting the connection of various types of external devices thereto, to satisfy usage requirements and enhance the user experience.
Currently, cell phones fail to effectively and accurately detect the impedance of an external device connected thereto. Therefore, they are merely capable of identifying few external devices.